The present invention relates to the art of tube manufacturing, particularly to an improved method and apparatus for upsetting tube ends.
When it is desired to make an end-to-end connection of two different-sized tubes, it is often found desirable to upset the end of one of the tubes. This involves heating the end of the tube and applying a compressive force to the heated end causing the tube wall to thicken. The shape of the resultant tube end can be controlled by providing a mandrel inside the tube and a die on its outer surface to control the thickening to the appropriate amount and direction.
FIGS. 1 and 2 illustrate the typical method used in the prior art to carry out the upsetting operation. A long gripper clamp 22 is shown clamping a tube 24 whose end is to be upset. An upset die 20, which is normally made of hardened tool steel, is secured within gripper clamp 22 and engages the end of the tube 24. The gripper clamp 22 holds the tube 24 stationary during the upsetting operation, while the upset die 20 confines the tube end in order to prevent the outer diameter of the tube from increasing during upsetting.
A hydraulic cylinder 10 is provided for applying the upset force to the tube. The hydraulic pressure inside the cylinder 10 moves a piston rod 12 that extends from the cylinder. A mandrel 16 is rigidly mounted on the piston rod 12 and is sheathed along part of its length by an upset sleeve 14 that is fixed to the mandrel 16. The piston rod 12, the upset sleeve 14, and the mandrel 16 move together. During the upsetting operation, the mandrel 16 is inserted into the tube 24 so that the upset sleeve 14 engages the face of the end of the tube 24 thereby transmitting the upset pressure. In the arrangement shown, an internal upset results wherein the outer diameter of the tube remains unchanged while its inner diameter is reduced. Accordingly, the diameter of the mandrel is somewhat less than the original inner diameter of the end of the tube 24, but when the upset pressure is applied to the tube 24 by the sleeve 14, the inner diameter of the end of the tube 24 is reduced to the diameter of the mandrel 16.
In order to remove the tube 24 after upsetting, the gripper clamp 22 and upset die 20 are split along their centerline into two halves as shown in FIG. 2 so that the halves may be separated to allow tube removal. Since a rather high compressive force is applied to the tube during the pressure stroke of the upsetting operation, these split dies tend to open up allowing the tube to extrude outward between the die halves producing an extrusion fin. The extrusion fin must be subsequently reduced by grinding. Further, the extrusion causes excessive die wear and rapid wear out.
The above-mentioned problems associated with tube upsetting would be eliminated thru the use of one-piece dies. Previous attempts at using one-piece dies have proven unsuccessful because the rather high compressive force required to upset the tube end resulted in the tube binding and thereby locking in the die and preventing removal without destroying the die.